Sublimation apparatus



April 24, 1956 R. KRoHN ETAL SUBLIMATION APPARATUS 3 Sheets-Sheet lFiled Sept. 9, 1944 alii.,

April 24, 1956 R. KROHN ET AL SUBLIMATION APPARATUS 3 Sheets-Sheet 2Filed Sept. 9, 1944 April 24, 1956 R. KROHN ET Al. 2,743,168

SUBLIMATION APPARATUS Filed Sept. 9, 1944 I5 Sheets-Sheet 5 UNH Mdm

United States Patent 2,743,168 SUBLIMATKION APPARATUS ApplicationSeptember 9, 1944, Serial No. 553,446

` 6 Claims. (Cpl. 23a-264) This invention relates to a sublimationprocess and apparatus. More particularly, this invention concerns aprocess and apparatus especially adapted for the treating of 'uraniumcompounds such as the halogen derivatives thereof to obtainpurification, the formation of a desired crystal structure and otherimprovements in the compounds, Vand is related to the copendingapplication of Hecker, Serial Number 552,557.

In general, the use of sublimation processes in the industry is old andwell known, and a number of processes and systems have been proposed inthe prior art. For example, the treatment of materials such asmagnesium, aluminum chloride, and the like has been carried out byprocedures wherein these materials are subjected to sublimation for theseparation or purification thereof. Theapparatus was comprised of tubesor retorts surrounded 'by a furnace or other heating device forvolatilizing the materials being sublimed. The aforementioned parts areconnected with condensing devices for collecting the sublimed materials.

More elaborate processes and apparatus have been developed particularlyas respects the processing of magnesium materials. In .suchconstructions the condensing units have'been provided with bafes,removable liners, and other refinements. The sublimation apparatus hasin many instances `been of a vertical type requiring the use of anoverhead crane or comparable device for the opening thereof duringcharging or for other purposes.

Some of the devices and processes of the prior art have not .beensusceptible to speedy or ei'lcient large scale continuous operation.Also, many of the devices are not suitable for the processing of uraniummaterials because of the refractory nature of this element, and the harddeposits Vwhich may be formed. In processing uranium materials there isthe possibility of the formation `of undesiredamorphous sublirnateunless the characteristics of the sublimation, conditions andcondensation are controlled in a certain manner.

Certain vertical sublimation equipment and processes of operation havebeen proposed by others working closely .in the feldof the presentinvention. The present con- 1 struction is believed to constitute animprovement over these last-mentioned sublimation units and processes ingreater speed of operation, greater adaptability to large scaleproduction, and capability of forming a high grade crystalline productparticularly suitable for use in certain processes wherein there is ademand for a highA quality uranium halide of the type producible byour-process and apparatus We have discovered an improved sublimationapparatus and process that is particularly suited lfor the sublimationVtreatment of uranium materials, exemplified by the production ofpurified high grade crystalline uranium chloride.

This invention has for a general object to improved sublimation processand apparatus.

Another object is to provide a sublimation apparatus provide an that hasimproved characteristics from the standpoint of ease of'operation, speedof operation, and freedomV from excessive maintenance.

Still another object is to provide a sublimation appara- Y tus that may'be constructed without extreme requirements as to lmechanical tolerancesin certain parts yet be used under conditions of exactingspecifications.

Another object is to provide an apparatus that isadapted to operateunder reduced pressure conditions together with an arrangement of partsfor obtaining the aforementioned reduced pressure.

Still another and particular object is to provide an apparatus that isespecially suitable for use in the processing of uranium materials. 'l

Still another object is to provide an apparatus ofthe aforementionedtype wherein the resultant sublimed materials maybe obtained lin theform of large homogeneous crystals which product isrstable underrelatively dry conditions. Y

Still another object is to provide an apparatus of the type describedthat is adapted to operate in conjunction with a vacuum system and whichcooperates therewith in a manner so that the pumpingoils and othercomponents of the vacuum system have a longer life and are subjectl tofeweroperational difficulties.

Another object of this invention is to provide an improved process forsublimation.

Still another object is to provide a sublimation process for applicationto uranium materials particularly haloin detail hereinafter.

For further understanding of our invention, reference is made to theattached drawings forming a part of the present application. In thedrawings, Fig. l is a semidiagrammatic side-elevation view of thecomplete sublimation apparatus `assembly in which certain parts arebroken away-and other parts shown in section for clarity.

Fig. 2 Vis a sectional view of the condenser portion ofV apparatus takenon the line A A of Fig. 3.

Fig. 3 is an end view of the-aforementioned condenser unit which certainparts have been shown in section for clarity.

Fig. 4 is a detailed view of the boat assembly for holding the charge.

Fig. k5 is an end view of the complete assembly.

Fig.` k6 is a side elevation view of the complete apparatus similar toFig. l, but showing in particular the manner in which the heating unitmay be placed in position lor re- Referring now toFig. l, referencenumeral 2 represents a movable electric furnace. ing'member 8, thisfurnace 2 may be moved into and out of position as better shown in Fig.6

The furnace may be of conventional construction including suitableelectric heating elements indicated at 3, insulation at 4, and variousother usual parts for the construction and operation of electricfurnaces. Wheels 6, which move on track 7, may be provided forpermitting larented apr. a4, rese.

For-encompassing protrudthenovement of the furnaceinto and out ofposition as^already referred to;l Thefurnace Zmay bemov'ed' out ofposition for cooling, repair, and other similar purposes.Theipr'otruding member 8 houses the charge boat 9, the `lat'ter"beingbetter 'shownfin Fig.V 4.' "Member `8`is connected to""a condenserstructure' 11'of special design,

better shown. in Fig. 2.

`Thecond`en`ser 1'1, by means of conduit 12,' is' connected to onel'or'rnore mechanical vacuum pumps (notV shown),

the trapsjl, 14,"15, and 20,.gaugesand the like employedv in anefficient vacuumpsystem. 4While' the particular vacuum's'ystem employedis 'not a limitation on the present invention', one'arrangementcomprising several different types "of vacuum apparatus, whichhas beenfound to'give good results is described herein; VThe"vaciinicn`s`ystemVVpreferably includes various lcontro1`.devices (not shown)` suchvas'Pirani gauges, ionizationgauges and the like.

The particular vacuum .systememployed in the present' embodiment'comprisesjthreesources `of reduced pressure.- That is the sublimation.system may be intercon-r nected'throughfvalve 17 and 'trap k14toarnechanical pump such'as a Kinney pump (not shown); Or the system maybeconnectedthrough the valve 16 and ytrapsl V16 :and 20 toai'oughing pump(notshown). f For .very low reduced, pressure, the'systemV may beconnected, by

closed thereby throwing the pressure reduction onto the f mechanicalpump. After a preliminary heating to be described more fully, valve 17,is closed andv valve 1 6 opened, traps 15 and 20 having vbeen filledwith-a cooling medium as indicated in connection with traps 13 and 14.Thelsystem is then on the roughing pump. During. this period trap 13 maybe de gassed and Vtrap 1'4. removed and cleaned and replaced. After'thscycle, v'traps 13 and`14 are refilled, valve 16 closed, valve,17 openedthrowingvthe system back :on the mechanical pump.

. Thereafter by closing valve 17 and opening valves 1 .8 and 2,5, thediffusion'pum'p lmaybe cutinto the system. l

Referring now to Fig. '2, the condenser, 11 yincludes an inner liner 2,1wholly disconnected'from' the outer 24, the entire liner 21 may bepulled out of or removed the boat.

v shell l22. By imbolting the condenser closure orV head fromtheapparatus'. This is advantageous in handling hygr'oscopic materials.Asindicated, the outside? of the'` condenser '11 is provided v'with anumber of cooling 'coils V23 of conventional design which may beconnected toVv I.water lines' through detachable connections.' a

Withinthc liner 21 but attached thereto is the conL volute o'rspiralmember 26, better 'showni'n' Fig. 3. This member functions'tocause thevapor tomove in an elongatedyspiral path. Also, the metal member'acts asa hot condenser as lwillbe further described in connection with thefunctioning ofthe apparatus. v f

Theliner `21 fits 'within' the apparatus' agaist'boat V9 in asubstantially vapor tight manner by means fof the interposed sealing`ring constructionl27`. VY'1`liisringf27 is similar'V toan expansibleautomotive'A piston ring, and by expandingl against 'theinterio'rsurface of member 8 gives a tightfjoin't withoutthenecessity' of'special machining" The boat 9 previously referred to, and shown in Fig.4,'is"in etecta cylindrical tank with a portion cut away" as indicatedat 10. The boat may be constructed from corrosion and heat resistantmaterial such as the com-` mercially obtainable material Hastelloy, orother high nickel alloy. Y

Referring now to the various incidental parts, Vthe traps 13, 14, 15,and 20V arer conventional liquid rair or liquid nitrogen traps. They areadapted to contain a bulb into which may be introducedv the liquidfreezingjmedium"V which causes the condensation of condensables as theypass out of the Vapparatus through the conduit 12.. I'

The 'protruding member 8'and the condenser 11 as well as variousr other`.parts are preferably'constructed from corrosion and heat resistantsteel as for example certain well known-stainless steel compositions.Such steels include chromium and nickel and preferably include inaddition a small content of anotheralloying element suchf as molydenurn,colurnbium, tungsten, titanium,

orthe like.. v'lhefvarious parts between the" condenserA and'the'sourcesof reduced pressure, as'for example c'o'iilif nicncing with conduit 12,maybeconstructed from or-..

dinary steel Aor `other standard material usual for vthe'conl structionofthe particular part.'

T he functionin'gof the apparatusrwill be described VbyLf- Y consideringthat the furnace portion has been pulled` otl asfindicatedin Fig. 6.Also, it will be considered that the` condenser head 24 has been removedand that the liner 21 'and other parts within the-'apparatus have beentaken out.V f e j The boat 9 is filled with'a charge (100-225 lbs.) of,for example, auranium chloride which it is desired Vto-' process Vinaccordance with the present invention. The boat is slid into theprotruding member 8 to the back thereof.; Then theA sealing ring, namelyring 27, is in' serted into :the front of the condenser' and pushedback` into member 8 so that the ring closely abuts the end of inasmuchas the ring `expands against the inner surface of 8, Vit effectivelyseals the'boat inthe end Y the apparatus so that the vaporsdo notpenetrate between the liner'and the condensenj The liner is next pushedintoV place through the front of the apparatus so e' that it abuts theaforementioned sealing ring 27. Byhis construction, asalready indicated,it is possible togob tain a satisfactory vapor-tight fit without thenecessity of special machining or requiring the construction of the:kparts to within a particularly close tolerance. The cover plate 28 isinserted and secured in place.- The head 24r of the condenser is boltedin place, 'andthe various coup 4 lings to the water-connections and thelike made. The traps 13 and 14 are thenlled with cooling ymedium such asliquidnitrogen. The mechanicalvacuum-pump-r is connected into the systemby opening the-valve -17- y Y slowly, then fully, and the system pumpedvdown very' A entrapperl gases or other volatiles removable byreduced' Yof the various parts. This is an important feature, othei" wise-vaporsmight penetrate between the`lin`er and vthe interiorV of thecondensercausing the :linerto freeze in the equipment. Also'fby this constructionit is notrequired that the liner be fitted with 'extreme care within-I Ycondenser 22, Y andl slight 'clearance may be allowed to permit easyremoval;V The liner is, however, 'in sufficientlyv close associationwiththe condenser so that heat transfer l thereto bybolts indicated at29.

slowly to about-one-tenth millimeter of mercury pressurer It isdesirable that the rate of reducing the pressure at thestart of theprocess be slow in order to preventfsolid particles from beingcarriedYover into the vacuum system 'mechanically `After the preliminaryreduction in pressure, the pump may be permitted to run at full rate forat least l5 minutes :to degas the charge. That is, air,-

pressure are pumped out. The degassing is` facilitated#- by raising thetemperature of the charge materials as"Jv` indicatedV inthe nextstcp.V'f

The heater 2 is then rolled into place as shown in Fig. 1, y and thecurrent turnedvon, slowly raising the -furnace" temperature toapproximately 250"Y C. The temperature range, namely, thefurnacetemperature is Vbetween ap# proximately 250i C. and 450 C., and a periodof abouttwo hours would be employed for carrying out the ini--v tialheating. During approximately the next two Vhours of heating, fthe!temperature of the lfurnace is permitted to rise to between 550 C.,and650."C. g.

During fthis'- later` heating period; `valve- 17 is?v clos'd anddensation of amorphous product.

valve16 on the roughing line is opened. In order to clean thesystem ofmaterials stopped by trap 13, the liquid air isremoved from trap 13 thensteam is introduced into trap 13 so that condensate such as HCl, COClzand the like, is volatilized out through the roughing line, andrecondensed in liquid air traps 15 and 20 if desired. The

liquid air traps are again filled with either liquid nitrogen or liquidair and the system again connected onto the mechanical pump by closingvalve 16 and opening valve 17. The reduction in pressure is continueduntil it is sufficiently low to permit cutting in the diffusion pump 31by opening valves 18 and 25.

The temperature of the furnace is now within the range of approximately700 C. to 825 C., and the ultimate degree of reduced pressure at the topof the diffusion pump would be of the order of 2 105 millimeters ofmercury. lIt is-not entirely essential that the system be placed 'underthis high degree of reduced pressure as sublimation of the uraniumhalides may be carried out under reduced pressure of the order of 30 or40 millimeters ofmercury. It is desirable, however, that a sucient'degree of reduced pressure be maintained as respects the particularmaterial being processed so that the system does not at any time passthrough the liquid phase. In other words, the uranium chloride shouldsublime directly and completely from the solid to the vapor. lf liquiduranium chloride forms in the system, because of its' corrosive action,the various metal parts may be corroded and injured. The magnitude ofthe temperature is not particularly critical, it merely being desirableto maintain adequate temperature for causing the materials to sublime.y`The temperature of the particular uranium chloride being described maybe raised to not more than about 586 C., namely the melting point ofUC14.

With the process functioning under the aforementioned temperature andpressure conditions, the vapors speedily pass out of the boat 9 into theinterior of the metal spiral 26, and then around the metal spiral. `Thismetal spiral 26 functions to cause the vapors to pass in an elongatedpath before theycan reach the-exit conduit 12. During theirpasvsage theybecome condensed on the metal spiral 26 inthe form of an excellentcrystalline product. This is V,obtained `by a warm or hot condensation,since the temperature of the metal spiral 26 is in this example between300 C.'400 C. That is, the condensation is relatively non-chilling ascompared with usual condensation. Such temperature is obtained by thepositioning of hthis metal spiral or baffle 26 at a predetermineddistance from the outer, water-cooled condenser surface. Since theVinterior of the apparatus is under reduced pressure, there ispractically no cooling by conduction. Consequently, the' spiral iscooled principally by radiation.

If the metal spiral is too cold, this will cause the con- By interposingthis metal spiral or convolute 26, practically all of the sublimedproduct is condensed out so that none passes out of the system throughconduit 12.

After the process has continued for a sufficient period (the entirecycle may consume eight to twelve hours or more) so that substantiallyall of the material in boat 9 has been sublimed, the furnace 2 may berolled off to the position indicated in Fig. 6, and the apparatuspermitted to cool. The apparatus is preferably slowly air cooled forabout three-quarters of an hour prior to the application of any severeexternal water-cooling. The cooling may be expedited by introducing adry, inert gas as nitrogen within the condenser chamber therebyproviding a medium through which the heat may be transferred byconduction. This may be accomplished by bleeding in nitrogen in aconventional manner through a nipple attached to the condenser or by'anyother suitable provision. After the equipment has cooled downsuiciently, the condenser head 24 is removed. The liner 21 may be pulledout, capped and taken to a dry box where the sublimate may be chippedout and placed in suitable containers. inasmuch as the purified,sublimed-product is hy'groscopic, it is desirable that the material bemaintained in a dry atmosphere.

Thereafter the apparatus may be cleaned as by washing,

' dried and another boat, ring, and liner inserted, and thesubstantially eliminated so that the pump oils employed in the vacuumsystem, as in the diffusion pumps, last several times longer. Inaddition, the product obtained by the process comprises large andhomogeneous crystals which are satisfactory for use in such processes asisotope separation.

Still further examples of our process applied to the sublimation ofuranium chloride are set forth below in tabular form. i

No. 1 N o. 2

Charge (crude) 148.2 lbs 196.5 lbs. Sublimation period.. Approx. 6%hrs.. l2 hours. Temperature 590 C. rising to Approx. 760 C. maxi- 700 C.mum Vacuum (final) 5 X 10-5 mm. Hg.. 3 X 105 mm. Hg. Overall time rs. 17hours. Yield (sublmat 183 lbs. Residue 6.5 lbs.

7 lbs.

The product obtained in the above examples was in the form ofhomogeneous crystals which were removed from the liner and placed incontainers. The process has been described as applied to the treatmentof uranium materials as the process has been found to give particu larlysatisfactory results in converting commercially produced uraniummaterial to a rened, high grade product. While our invention isparticularly adapted to the treatment of uranium materials, it may, ingeneral, be applied to the treatment of various other materialssusceptible of sublimation. For illustration there may be mentionedaluminum chlorides, iron chlorides, and certain organic compounds. Whenprocessing some of these other materials, it may be desirable that thecondensation be at a lower temperature as below 100 C. v

As indicated, certain of the temperatures referred to herein aredescribed as furnace temperatures. The temperature of thechargematerials lags below the furnace temperature. That is, thetemperature ofthe charge gradually rises from its temperature, as for example roomtemperature, as charged approaching the furnace temperature or reachingits volatilization temperature at which temperature the charge remainsuntil volatilized.

The degree of reduced pressure employed is generally below 50millimeters of mercury. The particular lower limit of reduced pressureis determined to some extent by the efficiency of the reduced pressuresystem. By means of the diffusion pumps and other parts described,reduced pressures of the order of 2 105 are obtainable. With other pumpsstill lower pressures may be obtained and used. In general, the functionof the reduced pressure is to eliminate air from within the apparatuswhich might oxidize the charge and also to provide a pressure underwhich sublimation occurs.

The term sublimation is employed herein in the conventional sense, andrefers to a process in which volatilizable materials are caused to passfrom the solid to the vapor phase without passing through the liquidphase.

In applying the process and apparatus to other matev rials havingdifferent melting points and other properties,

suitable adjustment would be made in the process for such differences.Alsochanges may be made inthe apparatus For example, referring to thecondenser and liner construction described as cylindricahzthisrmayv bemodified.

1: A sublimation apparatus adaptedlfor operationunderreduced-pressurewhich comprises@ movable heating unit, a,/condenserrfmember, a protruding member extending axially from thecondenser member, said protruding memberbeing of smaller diameterthansaidcondenser and o adapted lto bereceived in said heatingunit,means positioned in the protruding member` forreceiving a charge. to betreated, arliner and bafe positioned within said, condenser, said bafiieextending inwardly from said liner, ring means positioned between thecharge receiving rneans said condensen asY vand liner,'and means forreducing the pressurevyithin 2. A sublimation apparatus adapted foroperation under 1 reduced pressure which comprises a portable heatingunit,

- a condenser portion having a protruding member attached thereto andextending axially therefromL'Said protruding portion being adapted to behoused `by said heating unit, means for containing materials to betreated positioned within said protruding member, a liner and bafepositioned within the said condenser, said baffle extending spirallyinward from saidliner, and an expansive sealing ring positionedbetweenand engageable with the material containing means and liner` formaking a substantially vaportightseal between said liner and saidmaterial containing means.

VA sublimation apparatus which comprisesa condenser. member, a still incommunication with the ycondenser member, a movable heating unit forsaid still, a

container for receptionl of a charge, rsaid container positioned withinsaid still, a combination liner and substantiallytcoextensive spiralelement positioned within said condenser, `asealing ring Ameanspositioned between the container and liner, means for reducing thepressure within .said sublimation apparatus, and heat transfer, meansfor cooling said condenser. Y

I4. Asublimation apparatus which comprises a horizontally positionedmovable' heating unit, a condenser` member, an elongated stillprojecting outwardly from and` in-communication with thecondensermember, said still vbeing Sadaptedto be Vhoused in said heatingunit, aboat for the reception of chemical materials positioned in saidstill, a removable liner with a spiral element therein po-V sitionedwithin said condensensaid spiral elementv being substantiallycoextensive with and extending inwardlyY from the liner toward the Vaxisofy said condenser, a sealing means interposed between the boat and saidliner, and a plurality of cooling coils engageable with the condenserfor effecting a heat exchange relationship therewith.-v

5. Anapparatus of the class described which comprises a-tubular heatingunit, a condenser member having an elongated horizontally positionedextension defining ay still, at least a part of said still; beingadapted to be inserted in and housed by said heating unit, a charge re-Y ceivingboat positioned in said extension,'a removable liner withspiral shaped baffle zdisposed within said condenser, arsealing ringpositioned between the boat and liner, means forreducing the pressure`within lthe condenser, and va plurality vof cooling coils disposed`about7 Y thecondenser ifor effecting a heat transfer.

' Vw6.1 Anapparatusof theclassdescribed which co,n11`1rises,;V

a tubular movable heating unit, a'condensermember having an extensionprojecting therefrom for insertion intov said heating unit toV define astill, an elongated boat po-` sitionedwithin said extension to provideacontainer for charge materials, a removable liner having an internalspiral shaped bafe contained within said condenser, la sealing meanspositioned between the boat and liner andl f engageable with the innerwall of the condenser to-pre-.-

vent volatilized Ychemical Vmaterials ,fromv penetrating be,-4 tweensaidliner and condenser, means for reducing the pressure within thecondenser, and a plurality of cooling coils'in engagement with theouterwalls of the condenser to elect a heat transfer.V Y

' References Cited in the le of this patent UNITED STATES PATENTS1,662,070 Lyford v Mar. 13, 1928"- 1,888,996 Mclnerny et al Nov. 29,1932" 1,955,272 Carl et al Apr. 17, 1934 2,035,453 Betterton Mar. 3l,1936'vv 2,113,230 Ceccon APL 5, 1938r 2,258,374 Amati Oct. 7, 19412,289,328 Pechukas E July- 7, 1942 2,304,463v Maier Dec. 8, 1942 ,1.FOREIGN PATENTS 4 i 552,254`

'Homer f Peb. 5, *19241 Y Great Britain Mar. 370,

1. A SUBLIMATION APPARATUS ADAPTED FOR OPERATION UNDER REDUCED PRESSUREWHICH COMPRISES A MOVABLE HEATING UNIT, A CONDENSER MEMBER, A PROTRUDINGMEMBER EXTENDING AXIALLY FROM THE CONDENSER MEMBER, SAID PROTRUDINGMEMBER BEING OF SMALLER DIAMETER THAN SAID CONDENSER AND ADAPTED TO BERECEIVED IN SAID HEATING UNIT, MEANS POSITIONED IN THE PROTRUDING MEMBERFOR RECEIVING A CHARGE TO BE TREATED, A LINER AND BAFFLE POSITIONEDWITHIN SAID CONDENSER, SAID BAFFLE EXTENDING INWARDLY FROM SAID LINER,RING MEANS POSITIONED BETWEEN THE CHARGE RECEIVING MEANS AND LINER, ANDMEANS FOR REDUCING THE PRESSURE WITHIN SAID CONDENSER.